(1) Field of the Invention
The present invention relates to the displaying of information and particularly to the exercise of control over the size and content of a data display. More specifically, the present invention is directed to controllable display devices and to display manipulation control signal generators for use in such devices. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While all of the inventive aspects of the present invention are not limited to use in association with the display of data, the present invention is particularly well suited for use in and as a manipulatable information display. Accordingly, the invention will be discussed below in connection with the displaying of serially sensed information and particularly with respect to the manipulation of active visual displays.
The electronic display of graphical information, including information of the type which could conveniently be recorded by a pen on a moving chart, customarily involves the use of a cathode ray tube (CRT). As is well known, a CRT display will generate a visual spot at cartesian coordinance location x,y in response to corresponding voltage inputs of amplitudes x,y. To generate a graphical display, inputted voltage amplitudes x and y are varied to produce a visual image as defined by a plurality of serially generated spots or points. Thus, when the y input signal amplitude is varied linearly in time from y.sub.min to y.sub.max and the x input signal amplitude varies in an unknown manner between x.sub.min and x.sub.max, a trace will be produced with the changes in x input signal amplitude which occur during the time period between occurrence of the minimum and maximum y amplitude input signals. This generated trace will comprise a visually observable graphical display.
Continuing with the above discussion, by exercising control over the timing of the y input signal amplitude variation and suitably amplifying the x input signal amplitude, selected portions of the changes in the x input signal may be studied.
In the generation of a graphic display, as briefly described above, he laboratory equipment employed is commonly termed an oscilloscope when the x input signal is derived directly from a device or system under test. When the x input signal is generated electronically, particularly from stored data or patterns, the instrument which generates the graphic display is commonly termed a display or a display terminal. In either case, the prior art devices for generating graphics displays have possessed certain inherent deficiencies. These deficiencies will be described in more detail below in a discussion of prior art devices of the "display" type.
If data representing the amplitude of the x input signal is stored sequentially in a random access memory, the stored amplitude value at any point may be obtained by providing the address of that point at the address inputs of the memory. By converting the amplitude value at the addressed memory location to a voltage directly proportional to its value, an output voltage which may be displayed on a CRT will be provided. Addressing the memory sequentially will, of course, produce an output voltage which varies according to the sequentially stored data values. This output voltage may be used as the x input signal of varying amplitude to a display which also receives a y input signal which is changed in amplitude at each new sequential memory address. Thus, in the manner described briefly above, these x and y input signals will generate a graphic presentation of the data stored.
Given random access to the memory, it follows that all or any portion of the stored data may be displayed by selecting the memory addresses generated while the y input signal amplitude is varied. For example, if data is stored sequentially in 4096 memory locations, addressing locations 1 through 4096 in sequence to generate the x input signal while linearly changing the y input signal from y.sub.min to y.sub.max will provide a graphic presentation of all of the data in the 4096 memory locations. However, addressing memory locations 2049 through 4096 during the y.sub.min to y.sub.max amplitude transition will result in only the last half of the stored data being presented on the same display area formally occupied by all 4096 locations. Accordingly, amplitude variations in the last half of the stored data have been "expanded" by a factor of 2 on the display at the expense of losing the first half of the stored data from view. This is functionally analogous to the use of the ZOOM lens on a camera where details are expanded at the expense of the field of vision.
Continuing to discuss the camera analogy, moving the camera and its lens allows the user to SCAN the field of vision. Similarly, incrementing or decrementing the starting address location of the memory, while maintaining the same number of addresses accessed during the y amplitude transition, will SCAN the display through the data stored in the memory.
The stored x amplitude data values can range from x.sub.min to x.sub.max. Conversion of the digital signal commensurate with x.sub.max to an output voltage proportional thereto will result in generation of an image of maximum size. Some of the smaller stored data values, however, may be too small to be seen conveniently. By converting the stored data values to an output data range greater than that commensurate with x.sub.min to x.sub.max, all values will be displayed proportionally larger with the loss from view of those values exceeding the input x amplitude range; i.e., the RANGE or scale may be varied to enhance the readability of comparatively small stored data values.
The three above-discussed graphics manipulation functions; i.e., ZOOM, SCAN, and RANGE; may be implemented in a display by appropriate manipulation of data memory addressing and the data-to-voltage conversion. Prior to the present invention, displays have customarily treated these functions individually with separate controls. Thus, while attempting to examine the stored data as presented on prior art displays, the operator has been required to avert his attention in order to determine, locate and actuate the controls to cause desired changes in the display. Furthermore, the operator responses which have been required in the prior art in order to exercise control over the ZOOM, SCAN and RANGE functions of a display have had no correspondence with the resultant graphics change sought by the operator. Both of these disabilities of prior displays have greatly impeded their usefulness.